Stanford study cautions California billionaire tax could leave state with less revenue than expected
Reported by CBS News · October 19, 2026
A one-time wealth tax
Proposition 40 would apply a one-time state tax of 5% to billionaire wealth. The proposal was introduced by the Service Employees International Union-United Healthcare Workers West to raise billions of dollars for healthcare. The union did not immediately respond to a request for comment on the Stanford research.
Stanford economists warn of losses
The Stanford economists said the measure may raise about $30 billion, well below the $100 billion estimated by proponents. They said additional billionaires may have moved away quietly since the proposal was announced.
Voters split ahead of decision
A Citrin-Politico poll found that 46% of likely voters favor Proposition 40, while 43% oppose it. California voters are due to decide on the measure next month.
Key points
- Proposition 40 would impose a one-time 5% tax on billionaire wealth.
- Stanford economists estimate the tax could raise about $30 billion, compared with proponents’ $100 billion estimate.
- The economists estimate annual income-tax losses of $1 billion to $3.5 billion if billionaires leave.
- A poll found 46% of likely voters support Proposition 40 and 43% oppose it.